1. Field of the Invention
The present invention generally relates to manually operated joysticks and, in particular, to joysticks incorporating potentiometers.
2. Description of the Prior Art
A joystick is an apparatus for converting the manual input commands from a human operator into corresponding outputs that can be used to control the position of machines and the images in visual displays. A typical joystick has a control handle that is received in a ball and socket joint and can be manipulated in a solid angle by the operator. The joystick has a fixed mounting for its axis of rotation and outputs are generated according to the direction and the amount of inclination of the control handle.
In some joysticks the control handle is connected to two potentiometers through a linkage. Movement of the control handle is resolved by the linkage into two perpendicular directions. Motion in each direction is measured by a potentiometer and corresponding resistance values are generated. These resistance values are measured by a voltage dividing network. In other joysticks the control handle is connected to an inclination sensitive potentiometer. The inclination potentiometer type joystick measures the displacement of the control handle from the vertical and resistance values corresponding to this displacement are generated. These resistance values are also measured by a voltage dividing network.
Prior inclination potentiometers used in joysticks have either incorporated pendulums or have taken the form of electrolytic voltage sources. In the pendulum actuated potentiometers a heavy weight is attached to the wiper and swings the wiper across the resistance element during actuation. The input motion rotates the resistance element, and the heavy weight always seeks the vertical. The output of the potentiometer is a changing resistance that corresponds to the amount of inclination of the resistance element. In the electrolytic cell potentiometer a container having a plurality of plates is filled with an electrolytic solution. A voltage is developed across the cell by the chemical reaction between the plates and the solution. The plates have a geometry and are positioned within the container so that the plates are either immersed or withdrawn from the fluid as the container is inclined. Thus, as inclination of the cell varies the immersion of the plates, the voltage generated by the cell changes in a corresponding manner.
Heretofore potentiometer joysticks have tended to be expensive because a complex linkage was required in order to resolve the operator's manual input into motion of the wiper. In addition, most of these potentiometers have parts that must rub against each other and are thereby subject to wear. The contact between the resistance element and the wiper is also subjected to arcing where high voltages are used.
Joysticks incorporating inclination sensitive potentiometers have also tended to be expensive because of their complexity. In addition, those joysticks that incorporate pendulums are large in size and cannot be readily adapted into a small hand-held unit.